- Email: [email protected]
Devices Used in Cardiac Arrest
Devices Used in Card iac A rrest Steven C. Brooks, MD, MHSc, FRCPCa,b,c,*, Alina Toma, Jonathan Hsu, BHScf
MD, FRCPC
d,e
,
KEYWORDS Cardiac arrest Cardiopulmonary resuscitation Medical devices Extracorporeal life support
High-quality cardiopulmonary resuscitation (CPR), with an emphasis on adequate compression depth, rate, and consistency, is important in optimizing vital organ perfusion and survival from cardiac arrest.1 However, even the best-quality conventional CPR is inefficient, resulting in only 25% of normal cardiac output.2 Over the past several decades, many therapeutic devices have been designed to improve on conventional CPR and increase the probability of survival. This article does not provide a comprehensive review of all devices proposed for this purpose, but reports on a selection of those that have received attention in the medical literature and the most recent 2010 American Heart Association (AHA) guidelines for Emergency Cardiovascular Care and CPR.3 This article reviews devices in two main sections. The first section describes devices that are adjuncts to conventional manual chest compressions. These devices include those that provide prompts to the rescuer to guide conventional CPR. This section
This chapter discusses the several devices that may be used in the treatment of cardiac arrest. The ResQPod, Autopulse, Zoll Pocket CPR, Q-CPR, LUCAS, Lifestat, and ECMO devices are approved for use as described in this chapter. At the time of writing, the CPRGlove, Lifestick, ResQPump, and CPRmeter devices have not received FDA approval for use on patients in cardiac arrest as described in the chapter. The authors have nothing to disclose. a Division of Emergency Medicine, Department of Medicine, University of Toronto, 2075 Bayview Avenue, C7-53, Toronto, Ontario, Canada, M4N 3M5 b Rescu, Li Ka Shing Knowledge Institute, St Michael’s Hospital, 30 Bond Street, Toronto, Ontario, Canada, M5B 1M8 c Program for Trauma, Emergency and Critical Care, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5 d Department of Internal Medicine, Sunnybrook Health Sciences Centre, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario, Canada, M4N 3M5 e Emergency Department, St Michael’s Hospital, 30 Bond Street, Toronto, Ontario, Canada, M5B 1M8 f Undergraduate Medical Education Program, Faculty of Medicine, University of Toronto, Toronto, Canada * Corresponding author. Rescu, St. Michael’s Hospital, 30 Bond Street, Toronto, Ontario, M5B 1W8 E-mail address: [email protected] Emerg Med Clin N Am 30 (2012) 179–193 doi:10.1016/j.emc.2011.09.002 0733-8627/12/$ – see front matter Ó 2012 Elsevier Inc. All rights reserved.
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also reviews devices used to augment conventional manual chest compressions through improving the physics of the chest wall translation during the compression maneuver or improving the dynamics of the chest cavity pump through other mechanisms. The second section describes devices that have been designed to entirely replace manual chest compressions during CPR as a method of maintaining vital organ perfusion. DEVICES USED AS ADJUNCTS TO MANUAL CHEST COMPRESSIONS Devices Used to Prompt CPR Providers
CPR prompting devices are designed to focus the provider’s attention on accepted standards of CPR quality. Prompting devices range from basic metronomes to guide the rate of chest compressions to more sophisticated accelerometer or impedance technology that can provide real-time audio and visual feedback in response to other important components of CPR quality. Prompting devices are either stand-alone or incorporated into defibrillator-monitor units. Examples of stand-alone devices are the Zoll PocketCPR (Zoll Medical Corporation Technologies, Chelmsford, MA, USA) and the CPRmeter (Laerdal Medical, Stavanger, Norway), which are puck-like devices that can be placed under the hands of the rescuer during chest compressions. These devices measure aspects of dynamic chest compression and provide audio or video feedback. Prompting devices can be used on mannequins as educational tools during CPR training or as adjuncts during actual resuscitations. Metronomes
A metronome is a device used to mark time using an auditory or visual stimulus at regular intervals. The use of a metronome during CPR has been studied in the hospital and out-of-hospital settings. Most studies show that metronomes can improve the rate of chest compression delivery closer to recommended rates, and one study reported an associated improvement in survival.4–6 No studies have shown harm with the use of metronomes. Force transducers and accelerometers
Force transducers are devices that can measure the force applied to the chest wall during CPR. Accelerometers can detect movement of the chest wall. Data from these devices can be translated into audio or visual feedback on the depth, rate, consistency, and recoil of chest compressions. Supportive evidence for these devices was first reported in a case series of patients using a position-sensing arm that showed encouraging hemodynamic effects when used during in-hospital cardiac arrests. Abella and colleagues7 showed a reduction in variability of compression rate and ventilation rate in a prospective cohort study of 156 patients using the Q-CPR system (Philips Medical, Andover, MA, USA), which uses an accelerometer for feedback on compression depth and impedance measurements across the chest for feedback on ventilation rate. A prehospital before-and-after study of 284 patients performed with a similar device found that average compression depth increased from 34 9 mm to 38 6 mm (P<.001), percent of adequate depth compressions increased from 24% to 53% (P<.001), and mean compression rate decreased from 121 18 to 109 12 (P<.001).8 Survival was not significantly different between the groups, with 2.9% surviving to discharge versus 4.3% in the intervention group (P 5 .2). Edelson and colleagues9 also used the Q-CPR device in 224 patients and were able to show a decrease in ventilation rate (13 7 vs 18 8; P<.001) and an increase in compression depth (50 10 mm vs 44 10 mm; P<.001) when the device was used. Niles and colleagues10 were also able to show that audiovisual feedback in a pediatric
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arrest population decreases the amount of detrimental leaning performed during chest compressions and therefore promotes better chest recoil. When using an accelerometer, placing a stiff backboard behind the patient experiencing cardiac arrest is important for feedback. One study showed that the feedback can be inaccurate when chest compressions are performed on soft surfaces without a backboard, resulting in delivery of chest compressions with suboptimal compression depth.11 Accelerometer and pressure sensing technologies have also been incorporated into novel feedback devices, such as a CPR glove and CPR board. The CPR glove (Altreo Medical, Burlington, Ontario, Canada) is designed to be worn on the hand of the provider giving chest compressions. A small visual display and built-in speaker on the back of the glove provide the user with instructions on the sequence of CPR and feedback about quality of chest compressions. No studies reporting use of the glove have been published at the time of writing. A single Chinese case report described a pressure-sensitive CPR board placed under the patient’s body during CPR, which provides feedback about the quality of chest compresssions.12 No published studies have directly compared feedback devices. Devices Used to Augment Manual Chest Compressions Active compression-decompression devices
Active compression-decompression devices have been designed to improve the mechanics of standard chest compressions through facilitating an exaggerated recoil phase of the chest compression cycle. For example, the CardioPump ACD-CPR Device (Advanced Circulatory Systems, Inc., Roseville, MN) uses a suction cup component that attaches to the patient’s chest and allows lifting of the chest wall beyond neutral position causing active decompression (Fig. 1). This device also includes a force gauge to encourage adequate compression and decompression by the user. Other more simple devices, such as a modified oven mitt with Velcro, have also been developed for this purpose.13 The intended physiologic mechanism common to all active
Fig. 1. The CardioPump ACD-CPR Device (Advanced Circulatory Systems, Inc., Roseville, MN, USA) is an active compression-decompression CPR device that uses a suction cup to facilitate active decompression during the recoil phase of manual chest compressions during cardiac arrest. (Courtesy of Advanced Circulatory Systems, Inc., Roseville, MN, USA; with permission.)
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compression-decompression CPR (ACD-CPR) devices is to create a negative intrathoracic pressure and increased venous return during the active decompression phase. Several studies have shown that improved hemodynamics are possible with this technique compared with standard chest compressions.14 Evidence for the effectiveness of these devices in humans is mixed, but no data suggest they are harmful.15–27 A Cochrane systematic review and meta-analysis (updated in 2010) pooled the data from 12 randomized and pseudo-randomized comparisons involving 4988 patients and found no evidence of mortality benefit with the use of ACD-CPR compared with standard manual chest compressions.14 The recent American Heart Association (AHA) guidelines for CPR and Emergency Cardiovascular Care concluded that evidence is insufficient to recommend for or against the routine use of these devices in cardiac arrest, but suggest that these may be considered for use when providers are adequately trained and monitored. Impedance threshold device
During the compression phase of CPR, pressure in the heart chambers and intrathoracic vascular structures increases as external pressure is applied to the chest. The pressure gradient directs blood out of the heart and to the periphery. The recoil of the chest wall during the decompression phase is equally important. The decrease in intrathoracic pressure to subatmospheric levels assists in the venous return of circulation to the heart. This phase is critical for cardiac preload and is thus essential for optimal cardiac output, blood pressure, and vital organ perfusion. However, as the intrathoracic vacuum draws blood back to the heart, it simultaneously draws air into the lungs. This influx of inspiratory gases takes away from the potential hemodynamic benefit of the decompression phase of CPR. First described in 1995,28 the impedance threshold device (ITD) is designed to limit this influx of air, increase the negative intrathoracic pressure, and thus enhance circulation during CPR. This device is commercially available as the ResQPOD ITD (Advanced Circulatory Systems, Inc., Roseville, MN) (Fig. 2). The ITD is a pressuresensitive valve that can be attached to the respiratory circuit via an endotracheal tube, supraglottic airway, or facemask. The negative intrathoracic pressure in an intubated patient has been documented to be up to –13 mm Hg, contrasted with a pressure of only –3 mm Hg without the use of an ITD.29 When used with a facemask, a tight seal between the face and the mask must be continuously maintained during CPR to hold the vacuum. A two-person ventilation technique can be used to maintain this continuous seal, with one person delivering ventilations and another securing the mask against the patient’s face. Because of its flexibility in attachment to the respiratory circuit and its portable nature, the ITD is appropriate to use for basic life support in the field and for emergency department resuscitation. During individual chest compressions, air is allowed to move freely out of the chest and through the device, just as during active ventilation by the rescuer. The lumen within the ITD will remain open, creating no resistance to ventilation. Spontaneous inspiration through the ITD is possible but may be difficult for a recently resuscitated patient. Thus, immediate removal of the ITD once pulse has been restored is recommended. Besides providing augmentation of negative intrathoracic pressure during CPR decompression to increase venous return, the ResQPOD ITD comes equipped with ventilation timing assist lights that flash at a rate of 10 times a minute to prevent overventilation. Studies have shown that even professional rescuers responding to out-ofhospital cardiac arrests may excessively ventilate patients,30 which can lead to decreased venous return to the heart, decreased coronary perfusion pressure, and increased intracranial pressure.
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Fig. 2. The ResQPOD impedance threshold device (Advanced Circulatory Systems, Inc., Roseville, MN, USA) is used on the patient’s airway to prevent passive influx of respiratory gases during the recoil phase of chest compressions and increase the negative intrathoracic pressure generated. (Courtesy of Advanced Circulatory Systems, Inc., Roseville, MN, USA; with permission.)
A systematic review and meta-analysis published in 2008 identified five randomized controlled trials that tested the effectiveness of the ITD in treating out-of-hospital cardiac arrests. The included studies were heterogeneous in that three of them included the use of ACD-CPR in the ITD group and two used conventional CPR. The meta-analysis of these studies found that patients in the ITD group were more likely to experience return of spontaneous circulation (relative risk,1.29; 95% CI, 1.10– 1.51) and early survival, defined as survival at 24 hours or intensive care unit admission (relative risk, 1.45; 95% CI, 1.16–1.80). No evidence showed a positive effect on neurologic outcome in survivors or longer-term survival (eg, survival to hospital discharge). The 2010 AHA guidelines suggested that an ITD may be considered as a circulatory adjunct during CPR by trained personnel in adults in cardiac arrest.1,3 The moderate strength of recommendation (level IIb) balances the biologic plausibility for benefit with ITD use and the heterogeneous results from clinical studies. Soon after these guidelines were published, preliminary results from the Resuscitation Outcomes Consortium (ROC) PRIMED study were published in abstract form.31 The PRIMED study was a large multicenter, double-blind, randomized, controlled trial comparing the ITD with a sham device during standard CPR for patients experiencing
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nontraumatic out-of-hospital cardiac arrest. More than 8700 patients were randomized in this study. The Data Safety and Monitoring Board stopped the trial early because of futility. No difference was seen between groups regarding the primary outcome of survival to discharge with a good neurologic function (modified Rankin score 3). At the time of writing, full analysis of the study, including that of important subgroups, had not been published. Combined use of ACD-CPR and an ITD
Adding the use of an ITD during ACD-CPR may synergistically improve the effectiveness of chest compressions during resuscitation from cardiac arrest. In one small randomized controlled study in humans, airway pressures were not significantly reduced during ACD-CPR alone because inspiratory gases were allowed to flow into the airway during the decompression phase. When an ITD was used on an endotracheal tube during ACD-CPR, significant negative airway pressures were generated (mean, –7.3 mm Hg; SD, 4.5).29 Building on data from several smaller studies showing an improvement in short-term survival with combined ACD-CPR and ITD use, Aufderheide and colleagues32 recently published a multicenter randomized controlled study comparing the use of ACD-CPR with an ITD versus standard CPR without an ITD. In this study of more than 1200 patients who experienced nontraumatic out-of-hospital cardiac arrest, the investigators showed a 53% improvement in survival to hospital discharge with favorable neurologic function in the group treated with ACD-CPR and ITD. The study showed that 47 (6%) of 813 controls survived to hospital discharge with favorable neurologic function compared with 75 (9%) of 840 patients in the intervention group (odds ratio, 1.58; 95% CI, 1.07–2.36; P 5 .019). Similar results were found when assessing 1-year survival rates, with 9% in the ACD group and 6% of the standard CPR group (P 5 .03). Both survival groups had equivalent cognitive skills, disability ratings, and emotionalpsychological statuses. The overall major adverse event rate did not differ between groups, but more patients had pulmonary edema in the intervention group (94 [11%] of 840) compared with controls (62 [7%] of 813; P 5 .015). This study was well-designed but had some limitations. The ACD-CPR device (the ResQPump) also included a pressure gauge feedback device for providers to monitor chest compression quality, and the ITD device included a metronome light to standardize ventilation rate. These two additional sources of feedback should be considered cointerventions. Furthermore, the study was stopped early because of a funding shortage, and early termination of trials can lead to inflated estimates of outcomes.33 Lastly, the authors declared potential conflicts of interest, which include the fact that one is the coinventor of both tested devices and Chief Medical Officer of the company that sells the devices (Advance Circulatory Systems). Despite these limitations, in the context of previous studies showing the effective generation of negative intrathoracic pressure and numerous smaller clinical studies showing a short-term survival advantage, this study supports the concept that combining ACD-CPR and ITD to augment negative intrathoracic pressure generation is a viable strategy for resuscitating patients in cardiac arrest and may be associated with improved longer-term survival with good neurologic function. Reproduction of these results in future independent studies will clarify whether this strategy should be broadly implemented. Interposed abdominal compression devices
The Lifestick resuscitator (Datascope, Fairfield, NJ, USA) is a device that combines ACD-CPR and interposed abdominal compression techniques, which, when used in
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animal studies, showed an increased coronary perfusion pressure and total cerebral blood flow, higher end-tidal carbon dioxide, and better survival compared with standard CPR.34,35 One randomized trial and one prospective study investigated outcomes with the Lifestick device in patients experiencing cardiac arrest. The randomized trial included only 50 patients and was not powered to detect differences in survival outcomes, but it did show that the device was not associated with any increase in CPR-related injuries and was well accepted by users.36 The 2010 AHA guidelines for emergency cardiovascular care and CPR do not include a specific recommendation for the use of this type of device because there is insufficient data supporting or refuting effectiveness.3
Devices Used as an Alternative to Manual Chest Compressions Mechanical chest compression devices
Traditional cardiopulmonary resuscitation for cardiac arrest victims includes the delivery of rhythmic manual chest compressions by a human rescuer. However, several types of mechanical chest compression devices using a variety of mechanisms can provide an alternative to the human chest compressor, including pneumatic vests, load-distributing bands (LDB), and pistons. The feature common to all of them is that a deforming force is applied rhythmically and automatically to the chest wall, simulating the action of manual chest compressions. Numerous studies have shown that even well-trained, experienced rescuers tend to provide suboptimal compressions with respect to depth, rate, and consistency.37–40 Human chest compressors are also prone to fatigue and dwindling compression quality over time.41 In theory, mechanical chest compression devices are not susceptible to these problems. With the understanding that CPR quality and consistency are associated with patient outcomes, mechanical chest compression devices have been proposed as an alternative to imperfect manual CPR. The benefit of these devices may be their ability to provide consistent, high-quality chest compressions with minimal interruptions while liberating rescuers from this duty to tend to other tasks associated with resuscitation and transportation. Mechanical chest compression devices may be particularly useful in scenarios where a prolonged resuscitation may be necessary or where manual chest compressions may be technically difficult (eg, accidental hypothermia, toxicologic causes of cardiac arrest or intra-arrest cardiac catheterization). Available devices use a variety of mechanisms. Several papers report on the use of a pneumatic vest to facilitate chest compression during cardiac arrest. Similar to an oversized blood pressure cuff, the pneumatic vest is placed circumferentially around the patient’s thorax, and chest compression is achieved with the rapid introduction of pressurized air into and out of the vest.42 The pneumatic vest concept has since evolved into a load-distributing band cardiopulmonary resuscitation device called the AutoPulse (Zoll Medical Corporation, Chelmsford, MA, USA) (Fig. 3). The commercially available AutoPulse uses a wide band of material attached to a short backboard. The band is connected to a mechanism that can shorten the band under force in a rhythmic fashion such that the band squeezes the entire chest with each cycle. Other devices use compressed gas or an electric mechanism to drive a piston placed over the lower sternum of the patient. For example, the Life-Stat (formerly the Thumper) device (Michigan Instruments, Grand Rapids, MI, USA) is a gaspowered piston device with a built-in transport ventilator. Other piston devices, such as the Lund University Cardiac Assist System (LUCAS; Jolife AB, Lund, Sweden), incorporate a suction cup attachment for the piston to facilitate active compressiondecompression CPR (Fig. 4).
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Fig. 3. The AutoPulse Non-Invasive Cardiac Support Pump (Zoll Medical Corporation, Chelmsford, MA, USA) is a mechanical CPR device that uses a load-distributing band that encircles the patient’s chest and rhythmically shortens and lengthens to facilitate chest compressions. (Courtesy of Zoll Medical Corporation, Chelmsford, MA, USA; with permission.)
The relative effectiveness of mechanical chest compression devices as an alternative to manual chest compressions for improving clinical outcomes after cardiac arrest is not clear. Data suggesting clinical benefit with the use of mechanical chest compression devices are mostly derived from animal and human observational studies. Animal studies have shown that mechanical chest compressions can produce improved cerebral, central, and coronary blood flow43–45 and improved survival46,47
Fig. 4. The LUCAS2 (Jolife AB, Lund, Sweden) is a mechanical chest compression device that incorporates a suction cup attachment for the piston to facilitate active compressiondecompression CPR. (Courtesy of Jolife AB, Lund, Sweden; with permission.)
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compared with manual chest compressions. Several observational studies in humans have shown improved outcomes with the use of mechanical chest compression devices.48–52 The study by Ong and colleagues52 was a before-and-after comparison of the AutoPulse device with manual chest compressions in patients with out-ofhospital cardiac arrest treated by paramedics. When comparing 499 patients who received manual chest compressions with 284 patients who received treatment with the AutoPulse device, the authors showed an adjusted odds ratio of 2.27 (95% CI, 1.11–4.77) for survival to hospital discharge favoring the AutoPulse. They report a number-needed-to-treat of 15. The ASPIRE trial was published in the same issue of the Journal of the American Heart Association. In this multicenter, cluster-randomized trial, Hallstrom and colleagues53 studied 767 patients with out-of-hospital cardiac arrest. They compared the effectiveness of chest compressions delivered by the AutoPulse with that of standard manual chest compressions delivered during advanced life support and basic life support procedures by prehospital personnel. Clusters were based on ambulance station or group of stations, with crossover occurring at intervals ranging from 4 weeks to 2 months. The study recruited patients in five cities, and the protocol for CPR was not uniform across all sites. In fact, the CPR protocol was changed part way through the study at one site. The change involved a 2-minute delay in applying the mechanical device to the patient while paramedics administered manual CPR and a first defibrillation if needed. This change was incorporated in response to quality assurance data from the local emergency medical services system showing “prolonged time” without compressions in the load-distributing band device group. The primary outcome of this study was survival to 4 hours after the 911 call. The Data Safety and Monitoring Board stopped the trial early because of decreased survival to hospital discharge in patients who received mechanical chest compressions (9.9% in the manual CPR group vs 5.8% in the mechanical CPR group). The proportion of patients with a cerebral performance category of 1 or 2 (good neurologic function) at discharge was lower in the mechanical CPR arm of the study (3.1% in the mechanical CPR group vs 7.5% in the manual CPR group). The results of this study, which is the largest randomized comparison to date, were unexpected. The bulk of previous animal, human physiologic, and observational clinical data had suggested benefit. Many commentators and a more recent reanalysis of the original trial data54 suggested that the protocol change at one of the sites (resulting in a delay in the application of the device) had been responsible for the negative results. This controversy has highlighted the importance of how devices are incorporated into the sequence of CPR and the need to monitor CPR quality in both arms of the study. The risk is that the use of the devices may introduce interruptions in chest compressions or delay other interventions, such as defibrillations, which may negate any beneficial effects from the mechanical chest compressions that are ultimately provided once the device is in place. Reflecting on these heterogeneous data, the 2010 AHA guidelines for emergency cardiovascular care and CPR3 concluded that evidence is insufficient to recommend the routine use of mechanical CPR devices for cardiac arrest, but recommended that properly trained personnel may considered their use in specific settings of cardiac arrest. More clarity is likely to come soon from two ongoing, large, multicenter, randomized studies comparing mechanical chest compression with manual chest compressions. The PaRAMeDIC study in the United Kingdom (trial registered at http://www. controlled-trials.com/ISRCTN08233942) plans to randomize 4200 patients with outof-hospital cardiac arrest treated by paramedics to either chest compressions with
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the LUCAS device or manual chest compressions. They will measure survival to hospital discharge as the primary outcome, and a variety of neurologic and functional outcomes at short- and long-term end points as secondary outcomes. Enrollment is planned to end in 2013. The Circulation Improving Resuscitation Care (CIRC) study is a multicenter, randomized study enrolling patients with nontraumatic out-of-hospital cardiac arrest from several locations in the United States and Europe. This study will compare the use of the AutoPulse device with manual chest compressions with respect to survival to hospital discharge and several other outcomes, including neurologic outcome. The investigators are planning to recruit 5000 patients in the study, which will be completed sometime in 2012. The hope is that, with attention to uniform training, early application of the device into the sequence of CPR with minimal interruptions, and careful monitoring of CPR quality in both study arms, these trials will provide a definitive answer regarding the effectiveness of mechanical chest compression devices for cardiac arrest. Extracorporeal life support
Advances in technology have enabled the rapid deployment of cardiopulmonary bypass since it was first proposed in 1966.55 The extracorporeal membrane oxygenation (ECMO) device has shown to be effective in the neonatal population for respiratory failure56 and congenital cardiac defects.57 More recently, ECMO has been studied in chidren and adults with prolonged arrest after conventional measures have failed.58–61 A basic ECMO circuit consists of a gas-exchange device, such as an oxygenator; vascular cannulae to access and return blood; circuit tubing; a pump; and a heater– cooler that regulates blood temperature.62 ECMO is typically a temporary means of providing oxygenation, carbon dioxide removal, and hemodynamic support to patients with cardiac or pulmonary failure. In instances of cardiac arrest, this device can buy valuable time for resolution of underlying pathophysiologic problems. When ECMO is used on a patient, blood is removed from the venous system via a catheter, which can be attached to the right atrium. It passes through a membrane oxygenator and is delivered back to the patient’s circulatory system through a catheter in the arterial system. Points of attachment can be the aorta or common carotid artery. Besides the risk of complications, another challenge with ECMO is its deployment during ongoing conventional CPR. Interruptions in chest compressions should be minimized to facilitate favorable outcomes, including best possible coronary perfusion and chance of regaining spontaneous circulation. Thus, a rapid, simple cannulation technique is necessary. Choices for arterial cannulation include the carotid artery or femoral artery, and for venous cannulation include the internal jugular or the common femoral vein. Percutaneous cannulation of the femoral arteries during cardiac arrest has also been shown to be successful in adults.63 Although several observational studies and case reports have shown an association between extracorporeal life support for cardiac arrest and increased survival compared with conventional CPR,64,65 no data are available from randomized controlled trials. The emergent, unexpected nature of cardiac arrest and the complicated nature of deploying this intervention threaten the feasibility of a randomized controlled trial. In the most recent observational report from Seoul, Korea, Shin and colleagues65 undertook a retrospective analysis of 406 patients with in-hospital cardiac arrest. Using a propensity score–adjusted analysis, which attempted to control for prearrest conditions and CPR variables, the investigators observed that the use of ECMO in 120 adult patients who had greater than 10 minutes of CPR was associated with a reduced risk of mortality and less neurologic impairment (odds ratio, 0.17; 95% CI, 0.04–0.68).
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Currently, the practical deployment considerations and high resource use will prohibit the implementation of this therapy in most centers. Data are sparse and from nonrandomized comparisons, but support the feasibility, safety, and effectiveness of extracorporeal life support. The 2010 AHA guidelines found that evidence was insufficient to recommend the routine use of extracorporeal life support but that it may be considered when it is readily available for patients who have a brief period without blood flow and when the condition leading to cardiac arrest is reversible (eg, accidental hypothermia, drug intoxication).3 SUMMARY
Good-quality CPR and chest compressions are essential to maximize a patient’s chances of survival after cardiac arrest. Even the best manual chest compressions are inefficient at replacing normal cardiac output. This article reviewed several technologies and devices proposed to improve survival after cardiac arrest through optimizing the physics of CPR and vital organ perfusion. Despite promising results from laboratory studies or observational human studies, no single strategy or device has consistently shown improvement in survival over conventional CPR. Recent data supporting the combined use of the ITD and ACD-CPR in cardiac arrest32 provide rationale for investigating investigating combination strategies that simultaneously use multiple devices with complimentary mechanisms to improve cardiac output during CPR. The benefit of mechanical chest compression devices remains unclear. Evidence from randomized studies is mixed, with the largest study suggesting harm. Using these devices in cardiac arrest has the potential for delaying or interrupting good-quality manual CPR. For clinicians choosing to use any of these devices, caution and attention to overall CPR quality must be used during the deployment of devices. The answer to the long-debated question of whether human or machine provides the best life-saving chest compressions is likely to be answered shortly as two large randomized trials of mechanical chest compression close enrollment within the next 1 to 2 years. However, regardless of the results, this and other questions around the effectiveness of devices in the treatment of cardiac arrest will likely need to be readdressed continuously as technology and understanding of resuscitation advance. REFERENCES
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7. Abella BS, Edelson DP, Kim S, et al. CPR quality improvement during in-hospital cardiac arrest using a real-time audiovisual feedback system. Resuscitation 2007;73(1):54–61. 8. Kramer-Johansen J, Myklebust H, Wik L, et al. Quality of out-of-hospital cardiopulmonary resuscitation with real time automated feedback: a prospective interventional study. Resuscitation 2006;71(3):283–92. 9. Edelson DP, Litzinger B, Arora V, et al. Improving in-hospital cardiac arrest process and outcomes with performance debriefing. Arch Intern Med 2008; 168(10):1063–9. 10. Niles D, Nysaether J, Sutton R, et al. Leaning is common during in-hospital pediatric CPR, and decreased with automated corrective feedback. Resuscitation 2009;80(5):553–7. 11. Nishisaki A, Nysaether J, Sutton R, et al. Effect of mattress deflection on CPR quality assessment for older children and adolescents. Resuscitation 2009;80(5):540–5. 12. Wang LX, Zheng JC. Message measurement and feedback cardiopulmonary resuscitation board: a monitor for standard cardiopulmonary resuscitation. Zhongguo Wei Zhong Bing Ji Jiu Yi Xue 2010;22(2):73–5 [in Chinese]. 13. Udassi J, Udassi S, Lamb M, et al. Improved chest recoil using an adhesive glove device for active compression-decompression CPR in a pediatric manikin model. Resuscitation 2009;80(10):1158–63. 14. Lafuente-Lafuente C, Melero-Bascones M. Active chest compressiondecompression for cardiopulmonary resuscitation. Cochrane Database Syst Rev 2004;4:CD002751. 15. Goralski M, Ville´ger JL, Cami G, et al. Evaluation of active compressiondecompression cardiopulmonary resuscitation in out-of-hospital cardiac arrest. Reanimation Urgences 1998;7(5):543–50. 16. Mauer D, Schneider T, Dick W, et al. Active compression-decompression resuscitation: a prospective, randomized study in a two-tiered EMS system with physicians in the field. Resuscitation 1996;33(2):125–34. 17. Skogvoll E, Wik L. Active compression-decompression cardiopulmonary resuscitation: a population-based, prospective randomised clinical trial in out-of-hospital cardiac arrest. Resuscitation 1999;42(3):163–72. 18. Nolan J, Smith G, Evans R, et al. The United Kingdom pre-hospital study of active compression-decompression resuscitation. Resuscitation 1998;37(2):119–25. 19. Schwab TM, Callaham ML, Madsen CD, et al. A randomized clinical trial of active compression-decompression CPR vs standard CPR in out-of-hospital cardiac arrest in two cities. JAMA 1995;273(16):1261–8. 20. Luiz T, Ellinger K, Denz C. Active compression-decompression cardiopulmonary resuscitation does not improve survival in patients with prehospital cardiac arrest in a physician-manned emergency medical system. J Cardiothorac Vasc Anesth 1996;10(2):178–86. 21. Arai T, Adachi N, Tabo E, et al. Evaluation of efficiency of ACD-CPR and STDCPR; a multi-institutional study. Masui 2001;50(3):307–15 [in Japanese]. 22. Panzer W, Bretthauer M, Klingler H, et al. ACD versus standard CPR in a prehospital setting. Resuscitation 1996;33(2):117–24. 23. Kern KB, Figge G, Hilwig RW, et al. Active compression-decompression versus standard cardiopulmonary resuscitation in a porcine model: no improvement in outcome. Am Heart J 1996;132(6):1156–62. 24. Bertrand C, Hemery F, Carli P, et al. Constant flow insufflation of oxygen as the sole mode of ventilation during out-of-hospital cardiac arrest. Intensive Care Med 2006;32(6):843–51.
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25. Plaisance P, Lurie KG, Vicaut E, et al. A comparison of standard cardiopulmonary resuscitation and active compression-decompression resuscitation for out-of-hospital cardiac arrest. French Active Compression-Decompression Cardiopulmonary Resuscitation Study Group. N Engl J Med 1999;341(8):569–75. 26. Plaisance P, Adnet F, Vicaut E, et al. Benefit of active compressiondecompression cardiopulmonary resuscitation as a prehospital advanced cardiac life support. A randomized multicenter study. Circulation 1997;95(4): 955–61. 27. Shuster M, Lim SH, Deakin CD, et al. Part 7: CPR techniques and devices: 2010 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations. Circulation 2010; 122(16 Suppl 2):S338–44. 28. Lurie KG, Coffeen P, Shultz J, et al. Improving active compressiondecompression cardiopulmonary resuscitation with an inspiratory impedance valve. Circulation 1995;91(6):1629–32. 29. Plaisance P, Soleil C, Lurie KG, et al. Use of an inspiratory impedance threshold device on a facemask and endotracheal tube to reduce intrathoracic pressures during the decompression phase of active compression-decompression cardiopulmonary resuscitation. Crit Care Med 2005;33(5):990–4. 30. Aufderheide TP, Sigurdsson G, Pirrallo RG, et al. Hyperventilation-induced hypotension during cardiopulmonary resuscitation. Circulation 2004;109(16): 1960–5. 31. Aufderheide T, Nichol G, Rea TD, et al. The Resuscitation Outcomes Consortium (ROC) PRIMED Impedance Threshold Device (ITD) cardiac arrest trial: a prospective, randomized, double-blind, controlled clinical trial. Circulation 2010;122(21): S2225. 32. Aufderheide TP, Frascone RJ, Wayne MA, et al. Standard cardiopulmonary resuscitation versus active compression-decompression cardiopulmonary resuscitation with augmentation of negative intrathoracic pressure for out-of-hospital cardiac arrest: a randomised trial. Lancet 2011;377(9762):301–11. 33. Bassler D, Matthias B, Montori V, et al. Stopping randomized trials early for benefit and estimation of treatment effects. JAMA 2010;303(12):1180–7. 34. Tang W, Weil MH, Schock RB, et al. Phased chest and abdominal compressiondecompression. A new option for cardiopulmonary resuscitation. Circulation 1997;95(5):1335–40. 35. Wenzel V, Lindner KH, Prengel AW, et al. Effect of phased chest and abdominal compression-decompression cardiopulmonary resuscitation on myocardial and cerebral blood flow in pigs. Crit Care Med 2000;28(4):1107–12. 36. Arntz HR, Agrawal R, Richter H, et al. Phased chest and abdominal compressiondecompression versus conventional cardiopulmonary resuscitation in out-ofhospital cardiac arrest. Circulation 2001;104(7):768–72. 37. Abella BS, Alvarado JP, Myklebust H, et al. Quality of cardiopulmonary resuscitation during in-hospital cardiac arrest. JAMA 2005;293(3):305–10. 38. Abella BS, Sandbo N, Vassilatos P, et al. Chest compression rates during cardiopulmonary resuscitation are suboptimal: a prospective study during in-hospital cardiac arrest. Circulation 2005;111(4):428–34. 39. Ko PC, Chen WJ, Lin CH, et al. Evaluating the quality of prehospital cardiopulmonary resuscitation by reviewing automated external defibrillator records and survival for out-of-hospital witnessed arrests. Resuscitation 2005;64(2):163–9. 40. Wik L, Kramer-Johansen J, Myklebust H, et al. Quality of cardiopulmonary resuscitation during out-of-hospital cardiac arrest. JAMA 2005;293(3):299–304.
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41. Ashton A, McCluskey A, Gwinnutt C, et al. Effect of rescuer fatigue on performance of continuous external chest compressions over 3 minutes. Resuscitation 2002;55(2):151–5. 42. Halperin H, Tsitlik J, Gelfand M, et al. A preliminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest. N Engl J Med 1993;329:762–8. 43. Halperin H, Paradis N, Ornato JP. Improved hemodynamics with a novel chest compression device during a porcine model of cardiac arrest. Circulation 2002; 106:538. 44. Rubertsson S, Karlsten R. Increased cortical cerebral blood flow with LUCAS; a new device for mechanical chest compressions compared to standard external compressions during experimental cardiopulmonary resuscitation. Resuscitation 2005;65:357–63. 45. Timmerman S, Cardoso L, Ramires J. Improved hemodynamics with a novel chest compression device during treatment of in-hospital cardiac arrest. Prehosp Emerg Care 2003;7:162. 46. Ikeno F, Kaneda H, Hongo Y, et al. Augmentation of tissue perfusion by a novel compression device increases neurologically intact survival in a porcine model of prolonged cardiac arrest. Resuscitation 2006;68(1):109–18. 47. Steen S, Liao Q, Pierre L, et al. Evaluation of LUCAS, a new device for automatic mechanical compression and active decompression resuscitation. Resuscitation 2002;55(3):285–99. 48. Casner M, Andersen D, Isaacs SM. The impact of a new CPR device on rate of spontaneous circulation in out-of-hospital cardiac arrest. Prehosp Emerg Care 2005;9:61–7. 49. Steen S, Sjoberg T, Olsson P, et al. Treatment of out-of-hospital cardiac arrest with LUCAS, a new device for automatic mechanical compression and active decompression resuscitation. Resuscitation 2005;67:25–30. 50. Swanson M, Poniatowski M, O’Keefe M, et al. Effect of a CPR assist device on survival to emergency department arrival in out of hospital cardiac arrest. Circulation 2005;112(17):U1186. 51. Swanson M, Poniatowski M, O’Keefe M, et al. A CPR assist device increased emergency department admission and end tidal carbon dioxide partial pressures during treatment of out of hospital cardiac arrest. Circulation 2006;114(18):554. 52. Ong ME, Ornato JP, Edwards DP, et al. Use of an automated, load-distributing band chest compression device for out-of-hospital cardiac arrest resuscitation. JAMA 2006;295(22):2629–37. 53. Hallstrom A, Rea TD, Sayre MR, et al. Manual chest compression vs use of an automated chest compression device during resuscitation following out-ofhospital cardiac arrest: a randomized trial. JAMA 2006;295(22):2620–8. 54. Paradis N, Young G, Lemeshow S, et al. Inhomogeneity and temporal effects in AutoPulse Assisted Prehospital International Resuscitation—an exception from consent trial terminated early. Am J Emerg Med 2010;28:391–8. 55. Sawa Y. Percutaneous extracorporeal cardiopulmonary support: current practice and its role. J Artif Organs 2005;8(4):217–21. 56. Mugford M, Elbourne D, Field D. Extracorporeal membrane oxygenation for severe respiratory failure in newborn infants. Cochrane Database Syst Rev 2008;3:CD001340. 57. Aharon AS, Drinkwater DC Jr, Churchwell KB, et al. Extracorporeal membrane oxygenation in children after repair of congenital cardiac lesions. Ann Thorac Surg 2001;72(6):2095–102.
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58. Chen YS, Chao A, Yu HY, et al. Analysis and results of prolonged resuscitation in cardiac arrest patients rescued by extracorporeal membrane oxygenation. J Am Coll Cardiol 2003;41(2):197–203. 59. del Nido PJ. Extracorporeal membrane oxygenation for cardiac support in children. Ann Thorac Surg 1996;61(1):336–9. 60. Duncan BW, Ibrahim AE, Hraska V, et al. Use of rapid-deployment extracorporeal membrane oxygenation for the resuscitation of pediatric patients with heart disease after cardiac arrest. J Thorac Cardiovasc Surg 1998;116(2):305–9. 61. Ghez O, Feier H, Ughetto F, et al. Postoperative extracorporeal life support in pediatric cardiac surgery: recent results. ASAIO J 2005;51(5):513–6. 62. Royston D. Techniques in extracorporeal circulation. In: Kay PH, Munsch CM, editors. 4th edition. London: Arnold; 2004. p. 354. 63. Schwarz B, Mair P, Margreiter J, et al. Experience with percutaneous venoarterial cardiopulmonary bypass for emergency circulatory support. Crit Care Med 2003; 31(3):758–64. 64. Chen YS, Lin JW, Yu HY, et al. Cardiopulmonary resuscitation with assisted extracorporeal life-support versus conventional cardiopulmonary resuscitation in adults with in-hospital cardiac arrest: an observational study and propensity analysis. Lancet 2008;372(9638):554–61. 65. Shin TG, Choi JH, Jo IJ, et al. Extracorporeal cardiopulmonary resuscitation in patients with inhospital cardiac arrest: a comparison with conventional cardiopulmonary resuscitation. Crit Care Med 2011;39(1):1–7.
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KEYWORDS Cardiac arrest Cardiopulmonary resuscitation Medical devices Extracorporeal life support
High-quality cardiopulmonary resuscitation (CPR), with an emphasis on adequate compression depth, rate, and consistency, is important in optimizing vital organ perfusion and survival from cardiac arrest.1 However, even the best-quality conventional CPR is inefficient, resulting in only 25% of normal cardiac output.2 Over the past several decades, many therapeutic devices have been designed to improve on conventional CPR and increase the probability of survival. This article does not provide a comprehensive review of all devices proposed for this purpose, but reports on a selection of those that have received attention in the medical literature and the most recent 2010 American Heart Association (AHA) guidelines for Emergency Cardiovascular Care and CPR.3 This article reviews devices in two main sections. The first section describes devices that are adjuncts to conventional manual chest compressions. These devices include those that provide prompts to the rescuer to guide conventional CPR. This section
This chapter discusses the several devices that may be used in the treatment of cardiac arrest. The ResQPod, Autopulse, Zoll Pocket CPR, Q-CPR, LUCAS, Lifestat, and ECMO devices are approved for use as described in this chapter. At the time of writing, the CPRGlove, Lifestick, ResQPump, and CPRmeter devices have not received FDA approval for use on patients in cardiac arrest as described in the chapter. The authors have nothing to disclose. a Division of Emergency Medicine, Department of Medicine, University of Toronto, 2075 Bayview Avenue, C7-53, Toronto, Ontario, Canada, M4N 3M5 b Rescu, Li Ka Shing Knowledge Institute, St Michael’s Hospital, 30 Bond Street, Toronto, Ontario, Canada, M5B 1M8 c Program for Trauma, Emergency and Critical Care, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5 d Department of Internal Medicine, Sunnybrook Health Sciences Centre, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario, Canada, M4N 3M5 e Emergency Department, St Michael’s Hospital, 30 Bond Street, Toronto, Ontario, Canada, M5B 1M8 f Undergraduate Medical Education Program, Faculty of Medicine, University of Toronto, Toronto, Canada * Corresponding author. Rescu, St. Michael’s Hospital, 30 Bond Street, Toronto, Ontario, M5B 1W8 E-mail address: [email protected] Emerg Med Clin N Am 30 (2012) 179–193 doi:10.1016/j.emc.2011.09.002 0733-8627/12/$ – see front matter Ó 2012 Elsevier Inc. All rights reserved.
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also reviews devices used to augment conventional manual chest compressions through improving the physics of the chest wall translation during the compression maneuver or improving the dynamics of the chest cavity pump through other mechanisms. The second section describes devices that have been designed to entirely replace manual chest compressions during CPR as a method of maintaining vital organ perfusion. DEVICES USED AS ADJUNCTS TO MANUAL CHEST COMPRESSIONS Devices Used to Prompt CPR Providers
CPR prompting devices are designed to focus the provider’s attention on accepted standards of CPR quality. Prompting devices range from basic metronomes to guide the rate of chest compressions to more sophisticated accelerometer or impedance technology that can provide real-time audio and visual feedback in response to other important components of CPR quality. Prompting devices are either stand-alone or incorporated into defibrillator-monitor units. Examples of stand-alone devices are the Zoll PocketCPR (Zoll Medical Corporation Technologies, Chelmsford, MA, USA) and the CPRmeter (Laerdal Medical, Stavanger, Norway), which are puck-like devices that can be placed under the hands of the rescuer during chest compressions. These devices measure aspects of dynamic chest compression and provide audio or video feedback. Prompting devices can be used on mannequins as educational tools during CPR training or as adjuncts during actual resuscitations. Metronomes
A metronome is a device used to mark time using an auditory or visual stimulus at regular intervals. The use of a metronome during CPR has been studied in the hospital and out-of-hospital settings. Most studies show that metronomes can improve the rate of chest compression delivery closer to recommended rates, and one study reported an associated improvement in survival.4–6 No studies have shown harm with the use of metronomes. Force transducers and accelerometers
Force transducers are devices that can measure the force applied to the chest wall during CPR. Accelerometers can detect movement of the chest wall. Data from these devices can be translated into audio or visual feedback on the depth, rate, consistency, and recoil of chest compressions. Supportive evidence for these devices was first reported in a case series of patients using a position-sensing arm that showed encouraging hemodynamic effects when used during in-hospital cardiac arrests. Abella and colleagues7 showed a reduction in variability of compression rate and ventilation rate in a prospective cohort study of 156 patients using the Q-CPR system (Philips Medical, Andover, MA, USA), which uses an accelerometer for feedback on compression depth and impedance measurements across the chest for feedback on ventilation rate. A prehospital before-and-after study of 284 patients performed with a similar device found that average compression depth increased from 34 9 mm to 38 6 mm (P<.001), percent of adequate depth compressions increased from 24% to 53% (P<.001), and mean compression rate decreased from 121 18 to 109 12 (P<.001).8 Survival was not significantly different between the groups, with 2.9% surviving to discharge versus 4.3% in the intervention group (P 5 .2). Edelson and colleagues9 also used the Q-CPR device in 224 patients and were able to show a decrease in ventilation rate (13 7 vs 18 8; P<.001) and an increase in compression depth (50 10 mm vs 44 10 mm; P<.001) when the device was used. Niles and colleagues10 were also able to show that audiovisual feedback in a pediatric
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arrest population decreases the amount of detrimental leaning performed during chest compressions and therefore promotes better chest recoil. When using an accelerometer, placing a stiff backboard behind the patient experiencing cardiac arrest is important for feedback. One study showed that the feedback can be inaccurate when chest compressions are performed on soft surfaces without a backboard, resulting in delivery of chest compressions with suboptimal compression depth.11 Accelerometer and pressure sensing technologies have also been incorporated into novel feedback devices, such as a CPR glove and CPR board. The CPR glove (Altreo Medical, Burlington, Ontario, Canada) is designed to be worn on the hand of the provider giving chest compressions. A small visual display and built-in speaker on the back of the glove provide the user with instructions on the sequence of CPR and feedback about quality of chest compressions. No studies reporting use of the glove have been published at the time of writing. A single Chinese case report described a pressure-sensitive CPR board placed under the patient’s body during CPR, which provides feedback about the quality of chest compresssions.12 No published studies have directly compared feedback devices. Devices Used to Augment Manual Chest Compressions Active compression-decompression devices
Active compression-decompression devices have been designed to improve the mechanics of standard chest compressions through facilitating an exaggerated recoil phase of the chest compression cycle. For example, the CardioPump ACD-CPR Device (Advanced Circulatory Systems, Inc., Roseville, MN) uses a suction cup component that attaches to the patient’s chest and allows lifting of the chest wall beyond neutral position causing active decompression (Fig. 1). This device also includes a force gauge to encourage adequate compression and decompression by the user. Other more simple devices, such as a modified oven mitt with Velcro, have also been developed for this purpose.13 The intended physiologic mechanism common to all active
Fig. 1. The CardioPump ACD-CPR Device (Advanced Circulatory Systems, Inc., Roseville, MN, USA) is an active compression-decompression CPR device that uses a suction cup to facilitate active decompression during the recoil phase of manual chest compressions during cardiac arrest. (Courtesy of Advanced Circulatory Systems, Inc., Roseville, MN, USA; with permission.)
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compression-decompression CPR (ACD-CPR) devices is to create a negative intrathoracic pressure and increased venous return during the active decompression phase. Several studies have shown that improved hemodynamics are possible with this technique compared with standard chest compressions.14 Evidence for the effectiveness of these devices in humans is mixed, but no data suggest they are harmful.15–27 A Cochrane systematic review and meta-analysis (updated in 2010) pooled the data from 12 randomized and pseudo-randomized comparisons involving 4988 patients and found no evidence of mortality benefit with the use of ACD-CPR compared with standard manual chest compressions.14 The recent American Heart Association (AHA) guidelines for CPR and Emergency Cardiovascular Care concluded that evidence is insufficient to recommend for or against the routine use of these devices in cardiac arrest, but suggest that these may be considered for use when providers are adequately trained and monitored. Impedance threshold device
During the compression phase of CPR, pressure in the heart chambers and intrathoracic vascular structures increases as external pressure is applied to the chest. The pressure gradient directs blood out of the heart and to the periphery. The recoil of the chest wall during the decompression phase is equally important. The decrease in intrathoracic pressure to subatmospheric levels assists in the venous return of circulation to the heart. This phase is critical for cardiac preload and is thus essential for optimal cardiac output, blood pressure, and vital organ perfusion. However, as the intrathoracic vacuum draws blood back to the heart, it simultaneously draws air into the lungs. This influx of inspiratory gases takes away from the potential hemodynamic benefit of the decompression phase of CPR. First described in 1995,28 the impedance threshold device (ITD) is designed to limit this influx of air, increase the negative intrathoracic pressure, and thus enhance circulation during CPR. This device is commercially available as the ResQPOD ITD (Advanced Circulatory Systems, Inc., Roseville, MN) (Fig. 2). The ITD is a pressuresensitive valve that can be attached to the respiratory circuit via an endotracheal tube, supraglottic airway, or facemask. The negative intrathoracic pressure in an intubated patient has been documented to be up to –13 mm Hg, contrasted with a pressure of only –3 mm Hg without the use of an ITD.29 When used with a facemask, a tight seal between the face and the mask must be continuously maintained during CPR to hold the vacuum. A two-person ventilation technique can be used to maintain this continuous seal, with one person delivering ventilations and another securing the mask against the patient’s face. Because of its flexibility in attachment to the respiratory circuit and its portable nature, the ITD is appropriate to use for basic life support in the field and for emergency department resuscitation. During individual chest compressions, air is allowed to move freely out of the chest and through the device, just as during active ventilation by the rescuer. The lumen within the ITD will remain open, creating no resistance to ventilation. Spontaneous inspiration through the ITD is possible but may be difficult for a recently resuscitated patient. Thus, immediate removal of the ITD once pulse has been restored is recommended. Besides providing augmentation of negative intrathoracic pressure during CPR decompression to increase venous return, the ResQPOD ITD comes equipped with ventilation timing assist lights that flash at a rate of 10 times a minute to prevent overventilation. Studies have shown that even professional rescuers responding to out-ofhospital cardiac arrests may excessively ventilate patients,30 which can lead to decreased venous return to the heart, decreased coronary perfusion pressure, and increased intracranial pressure.
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Fig. 2. The ResQPOD impedance threshold device (Advanced Circulatory Systems, Inc., Roseville, MN, USA) is used on the patient’s airway to prevent passive influx of respiratory gases during the recoil phase of chest compressions and increase the negative intrathoracic pressure generated. (Courtesy of Advanced Circulatory Systems, Inc., Roseville, MN, USA; with permission.)
A systematic review and meta-analysis published in 2008 identified five randomized controlled trials that tested the effectiveness of the ITD in treating out-of-hospital cardiac arrests. The included studies were heterogeneous in that three of them included the use of ACD-CPR in the ITD group and two used conventional CPR. The meta-analysis of these studies found that patients in the ITD group were more likely to experience return of spontaneous circulation (relative risk,1.29; 95% CI, 1.10– 1.51) and early survival, defined as survival at 24 hours or intensive care unit admission (relative risk, 1.45; 95% CI, 1.16–1.80). No evidence showed a positive effect on neurologic outcome in survivors or longer-term survival (eg, survival to hospital discharge). The 2010 AHA guidelines suggested that an ITD may be considered as a circulatory adjunct during CPR by trained personnel in adults in cardiac arrest.1,3 The moderate strength of recommendation (level IIb) balances the biologic plausibility for benefit with ITD use and the heterogeneous results from clinical studies. Soon after these guidelines were published, preliminary results from the Resuscitation Outcomes Consortium (ROC) PRIMED study were published in abstract form.31 The PRIMED study was a large multicenter, double-blind, randomized, controlled trial comparing the ITD with a sham device during standard CPR for patients experiencing
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nontraumatic out-of-hospital cardiac arrest. More than 8700 patients were randomized in this study. The Data Safety and Monitoring Board stopped the trial early because of futility. No difference was seen between groups regarding the primary outcome of survival to discharge with a good neurologic function (modified Rankin score 3). At the time of writing, full analysis of the study, including that of important subgroups, had not been published. Combined use of ACD-CPR and an ITD
Adding the use of an ITD during ACD-CPR may synergistically improve the effectiveness of chest compressions during resuscitation from cardiac arrest. In one small randomized controlled study in humans, airway pressures were not significantly reduced during ACD-CPR alone because inspiratory gases were allowed to flow into the airway during the decompression phase. When an ITD was used on an endotracheal tube during ACD-CPR, significant negative airway pressures were generated (mean, –7.3 mm Hg; SD, 4.5).29 Building on data from several smaller studies showing an improvement in short-term survival with combined ACD-CPR and ITD use, Aufderheide and colleagues32 recently published a multicenter randomized controlled study comparing the use of ACD-CPR with an ITD versus standard CPR without an ITD. In this study of more than 1200 patients who experienced nontraumatic out-of-hospital cardiac arrest, the investigators showed a 53% improvement in survival to hospital discharge with favorable neurologic function in the group treated with ACD-CPR and ITD. The study showed that 47 (6%) of 813 controls survived to hospital discharge with favorable neurologic function compared with 75 (9%) of 840 patients in the intervention group (odds ratio, 1.58; 95% CI, 1.07–2.36; P 5 .019). Similar results were found when assessing 1-year survival rates, with 9% in the ACD group and 6% of the standard CPR group (P 5 .03). Both survival groups had equivalent cognitive skills, disability ratings, and emotionalpsychological statuses. The overall major adverse event rate did not differ between groups, but more patients had pulmonary edema in the intervention group (94 [11%] of 840) compared with controls (62 [7%] of 813; P 5 .015). This study was well-designed but had some limitations. The ACD-CPR device (the ResQPump) also included a pressure gauge feedback device for providers to monitor chest compression quality, and the ITD device included a metronome light to standardize ventilation rate. These two additional sources of feedback should be considered cointerventions. Furthermore, the study was stopped early because of a funding shortage, and early termination of trials can lead to inflated estimates of outcomes.33 Lastly, the authors declared potential conflicts of interest, which include the fact that one is the coinventor of both tested devices and Chief Medical Officer of the company that sells the devices (Advance Circulatory Systems). Despite these limitations, in the context of previous studies showing the effective generation of negative intrathoracic pressure and numerous smaller clinical studies showing a short-term survival advantage, this study supports the concept that combining ACD-CPR and ITD to augment negative intrathoracic pressure generation is a viable strategy for resuscitating patients in cardiac arrest and may be associated with improved longer-term survival with good neurologic function. Reproduction of these results in future independent studies will clarify whether this strategy should be broadly implemented. Interposed abdominal compression devices
The Lifestick resuscitator (Datascope, Fairfield, NJ, USA) is a device that combines ACD-CPR and interposed abdominal compression techniques, which, when used in
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animal studies, showed an increased coronary perfusion pressure and total cerebral blood flow, higher end-tidal carbon dioxide, and better survival compared with standard CPR.34,35 One randomized trial and one prospective study investigated outcomes with the Lifestick device in patients experiencing cardiac arrest. The randomized trial included only 50 patients and was not powered to detect differences in survival outcomes, but it did show that the device was not associated with any increase in CPR-related injuries and was well accepted by users.36 The 2010 AHA guidelines for emergency cardiovascular care and CPR do not include a specific recommendation for the use of this type of device because there is insufficient data supporting or refuting effectiveness.3
Devices Used as an Alternative to Manual Chest Compressions Mechanical chest compression devices
Traditional cardiopulmonary resuscitation for cardiac arrest victims includes the delivery of rhythmic manual chest compressions by a human rescuer. However, several types of mechanical chest compression devices using a variety of mechanisms can provide an alternative to the human chest compressor, including pneumatic vests, load-distributing bands (LDB), and pistons. The feature common to all of them is that a deforming force is applied rhythmically and automatically to the chest wall, simulating the action of manual chest compressions. Numerous studies have shown that even well-trained, experienced rescuers tend to provide suboptimal compressions with respect to depth, rate, and consistency.37–40 Human chest compressors are also prone to fatigue and dwindling compression quality over time.41 In theory, mechanical chest compression devices are not susceptible to these problems. With the understanding that CPR quality and consistency are associated with patient outcomes, mechanical chest compression devices have been proposed as an alternative to imperfect manual CPR. The benefit of these devices may be their ability to provide consistent, high-quality chest compressions with minimal interruptions while liberating rescuers from this duty to tend to other tasks associated with resuscitation and transportation. Mechanical chest compression devices may be particularly useful in scenarios where a prolonged resuscitation may be necessary or where manual chest compressions may be technically difficult (eg, accidental hypothermia, toxicologic causes of cardiac arrest or intra-arrest cardiac catheterization). Available devices use a variety of mechanisms. Several papers report on the use of a pneumatic vest to facilitate chest compression during cardiac arrest. Similar to an oversized blood pressure cuff, the pneumatic vest is placed circumferentially around the patient’s thorax, and chest compression is achieved with the rapid introduction of pressurized air into and out of the vest.42 The pneumatic vest concept has since evolved into a load-distributing band cardiopulmonary resuscitation device called the AutoPulse (Zoll Medical Corporation, Chelmsford, MA, USA) (Fig. 3). The commercially available AutoPulse uses a wide band of material attached to a short backboard. The band is connected to a mechanism that can shorten the band under force in a rhythmic fashion such that the band squeezes the entire chest with each cycle. Other devices use compressed gas or an electric mechanism to drive a piston placed over the lower sternum of the patient. For example, the Life-Stat (formerly the Thumper) device (Michigan Instruments, Grand Rapids, MI, USA) is a gaspowered piston device with a built-in transport ventilator. Other piston devices, such as the Lund University Cardiac Assist System (LUCAS; Jolife AB, Lund, Sweden), incorporate a suction cup attachment for the piston to facilitate active compressiondecompression CPR (Fig. 4).
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Fig. 3. The AutoPulse Non-Invasive Cardiac Support Pump (Zoll Medical Corporation, Chelmsford, MA, USA) is a mechanical CPR device that uses a load-distributing band that encircles the patient’s chest and rhythmically shortens and lengthens to facilitate chest compressions. (Courtesy of Zoll Medical Corporation, Chelmsford, MA, USA; with permission.)
The relative effectiveness of mechanical chest compression devices as an alternative to manual chest compressions for improving clinical outcomes after cardiac arrest is not clear. Data suggesting clinical benefit with the use of mechanical chest compression devices are mostly derived from animal and human observational studies. Animal studies have shown that mechanical chest compressions can produce improved cerebral, central, and coronary blood flow43–45 and improved survival46,47
Fig. 4. The LUCAS2 (Jolife AB, Lund, Sweden) is a mechanical chest compression device that incorporates a suction cup attachment for the piston to facilitate active compressiondecompression CPR. (Courtesy of Jolife AB, Lund, Sweden; with permission.)
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compared with manual chest compressions. Several observational studies in humans have shown improved outcomes with the use of mechanical chest compression devices.48–52 The study by Ong and colleagues52 was a before-and-after comparison of the AutoPulse device with manual chest compressions in patients with out-ofhospital cardiac arrest treated by paramedics. When comparing 499 patients who received manual chest compressions with 284 patients who received treatment with the AutoPulse device, the authors showed an adjusted odds ratio of 2.27 (95% CI, 1.11–4.77) for survival to hospital discharge favoring the AutoPulse. They report a number-needed-to-treat of 15. The ASPIRE trial was published in the same issue of the Journal of the American Heart Association. In this multicenter, cluster-randomized trial, Hallstrom and colleagues53 studied 767 patients with out-of-hospital cardiac arrest. They compared the effectiveness of chest compressions delivered by the AutoPulse with that of standard manual chest compressions delivered during advanced life support and basic life support procedures by prehospital personnel. Clusters were based on ambulance station or group of stations, with crossover occurring at intervals ranging from 4 weeks to 2 months. The study recruited patients in five cities, and the protocol for CPR was not uniform across all sites. In fact, the CPR protocol was changed part way through the study at one site. The change involved a 2-minute delay in applying the mechanical device to the patient while paramedics administered manual CPR and a first defibrillation if needed. This change was incorporated in response to quality assurance data from the local emergency medical services system showing “prolonged time” without compressions in the load-distributing band device group. The primary outcome of this study was survival to 4 hours after the 911 call. The Data Safety and Monitoring Board stopped the trial early because of decreased survival to hospital discharge in patients who received mechanical chest compressions (9.9% in the manual CPR group vs 5.8% in the mechanical CPR group). The proportion of patients with a cerebral performance category of 1 or 2 (good neurologic function) at discharge was lower in the mechanical CPR arm of the study (3.1% in the mechanical CPR group vs 7.5% in the manual CPR group). The results of this study, which is the largest randomized comparison to date, were unexpected. The bulk of previous animal, human physiologic, and observational clinical data had suggested benefit. Many commentators and a more recent reanalysis of the original trial data54 suggested that the protocol change at one of the sites (resulting in a delay in the application of the device) had been responsible for the negative results. This controversy has highlighted the importance of how devices are incorporated into the sequence of CPR and the need to monitor CPR quality in both arms of the study. The risk is that the use of the devices may introduce interruptions in chest compressions or delay other interventions, such as defibrillations, which may negate any beneficial effects from the mechanical chest compressions that are ultimately provided once the device is in place. Reflecting on these heterogeneous data, the 2010 AHA guidelines for emergency cardiovascular care and CPR3 concluded that evidence is insufficient to recommend the routine use of mechanical CPR devices for cardiac arrest, but recommended that properly trained personnel may considered their use in specific settings of cardiac arrest. More clarity is likely to come soon from two ongoing, large, multicenter, randomized studies comparing mechanical chest compression with manual chest compressions. The PaRAMeDIC study in the United Kingdom (trial registered at http://www. controlled-trials.com/ISRCTN08233942) plans to randomize 4200 patients with outof-hospital cardiac arrest treated by paramedics to either chest compressions with
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the LUCAS device or manual chest compressions. They will measure survival to hospital discharge as the primary outcome, and a variety of neurologic and functional outcomes at short- and long-term end points as secondary outcomes. Enrollment is planned to end in 2013. The Circulation Improving Resuscitation Care (CIRC) study is a multicenter, randomized study enrolling patients with nontraumatic out-of-hospital cardiac arrest from several locations in the United States and Europe. This study will compare the use of the AutoPulse device with manual chest compressions with respect to survival to hospital discharge and several other outcomes, including neurologic outcome. The investigators are planning to recruit 5000 patients in the study, which will be completed sometime in 2012. The hope is that, with attention to uniform training, early application of the device into the sequence of CPR with minimal interruptions, and careful monitoring of CPR quality in both study arms, these trials will provide a definitive answer regarding the effectiveness of mechanical chest compression devices for cardiac arrest. Extracorporeal life support
Advances in technology have enabled the rapid deployment of cardiopulmonary bypass since it was first proposed in 1966.55 The extracorporeal membrane oxygenation (ECMO) device has shown to be effective in the neonatal population for respiratory failure56 and congenital cardiac defects.57 More recently, ECMO has been studied in chidren and adults with prolonged arrest after conventional measures have failed.58–61 A basic ECMO circuit consists of a gas-exchange device, such as an oxygenator; vascular cannulae to access and return blood; circuit tubing; a pump; and a heater– cooler that regulates blood temperature.62 ECMO is typically a temporary means of providing oxygenation, carbon dioxide removal, and hemodynamic support to patients with cardiac or pulmonary failure. In instances of cardiac arrest, this device can buy valuable time for resolution of underlying pathophysiologic problems. When ECMO is used on a patient, blood is removed from the venous system via a catheter, which can be attached to the right atrium. It passes through a membrane oxygenator and is delivered back to the patient’s circulatory system through a catheter in the arterial system. Points of attachment can be the aorta or common carotid artery. Besides the risk of complications, another challenge with ECMO is its deployment during ongoing conventional CPR. Interruptions in chest compressions should be minimized to facilitate favorable outcomes, including best possible coronary perfusion and chance of regaining spontaneous circulation. Thus, a rapid, simple cannulation technique is necessary. Choices for arterial cannulation include the carotid artery or femoral artery, and for venous cannulation include the internal jugular or the common femoral vein. Percutaneous cannulation of the femoral arteries during cardiac arrest has also been shown to be successful in adults.63 Although several observational studies and case reports have shown an association between extracorporeal life support for cardiac arrest and increased survival compared with conventional CPR,64,65 no data are available from randomized controlled trials. The emergent, unexpected nature of cardiac arrest and the complicated nature of deploying this intervention threaten the feasibility of a randomized controlled trial. In the most recent observational report from Seoul, Korea, Shin and colleagues65 undertook a retrospective analysis of 406 patients with in-hospital cardiac arrest. Using a propensity score–adjusted analysis, which attempted to control for prearrest conditions and CPR variables, the investigators observed that the use of ECMO in 120 adult patients who had greater than 10 minutes of CPR was associated with a reduced risk of mortality and less neurologic impairment (odds ratio, 0.17; 95% CI, 0.04–0.68).
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Currently, the practical deployment considerations and high resource use will prohibit the implementation of this therapy in most centers. Data are sparse and from nonrandomized comparisons, but support the feasibility, safety, and effectiveness of extracorporeal life support. The 2010 AHA guidelines found that evidence was insufficient to recommend the routine use of extracorporeal life support but that it may be considered when it is readily available for patients who have a brief period without blood flow and when the condition leading to cardiac arrest is reversible (eg, accidental hypothermia, drug intoxication).3 SUMMARY
Good-quality CPR and chest compressions are essential to maximize a patient’s chances of survival after cardiac arrest. Even the best manual chest compressions are inefficient at replacing normal cardiac output. This article reviewed several technologies and devices proposed to improve survival after cardiac arrest through optimizing the physics of CPR and vital organ perfusion. Despite promising results from laboratory studies or observational human studies, no single strategy or device has consistently shown improvement in survival over conventional CPR. Recent data supporting the combined use of the ITD and ACD-CPR in cardiac arrest32 provide rationale for investigating investigating combination strategies that simultaneously use multiple devices with complimentary mechanisms to improve cardiac output during CPR. The benefit of mechanical chest compression devices remains unclear. Evidence from randomized studies is mixed, with the largest study suggesting harm. Using these devices in cardiac arrest has the potential for delaying or interrupting good-quality manual CPR. For clinicians choosing to use any of these devices, caution and attention to overall CPR quality must be used during the deployment of devices. The answer to the long-debated question of whether human or machine provides the best life-saving chest compressions is likely to be answered shortly as two large randomized trials of mechanical chest compression close enrollment within the next 1 to 2 years. However, regardless of the results, this and other questions around the effectiveness of devices in the treatment of cardiac arrest will likely need to be readdressed continuously as technology and understanding of resuscitation advance. REFERENCES
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